Abseil's Swiss Tables: A High-Performance Hash Table Implementation

Abseil provides a family of high-performance hash tables called Swiss Tables, including `absl::flat_hash_map`. These tables utilize a clever metadata scheme and SSE instructions for optimized lookups, resulting in significant performance improvements. Metadata consists of a control bit and a 7-bit H2 hash value to quickly filter candidate matches. Furthermore, Swiss Tables avoid unnecessary memory allocations and copies; `emplace` and `insert` operations leverage move semantics for optimal performance.